Summary — Aspects of the water relations of three oak species (Quercus gambelii, Q turbinella and Q macrocarpa) and their hybrids (Q gambelii x turbinella, Q gambelii x macrocarpa) were observed under common garden conditions in northern Utah, USA. In the absence of summer moisture inputs, Q macrocarpa and Q turbinella were unable to maintain active gas exchange through the day; following an early morning peak, leaf conductances to water vapor remained very low through the remainder of the day. In contrast, Q gambelii and the hybrids were able to maintain high leaf conductances throughout this period. Consistent with these observations, Q gambelii is thought to have a root system penetrating to the deeper, winter-recharged layers, a feature apparently absent in both Q macrocarpa or Q turbinella. Based on current hybrid distributions, both Q turbinella and Q macrocarpa once extended into drier more northerly regions than they occupy at present. When these parents retreated, they left behind hybrids with Q gambelii, which do not depend on monsoonal moisture input. Leaf size, leaf longevity, carbon isotope ratio, and minimum winter temperatures appear not to be correlated with the absence of Q macrocarpa and Q turbinella from summer-dry habitats. Instead it appears that reliance on summer monsoon events is one of the critical factors influencing loss of these oaks from summer-dry sites in the intermountain west.
In 1984, a survey was done to determine the distribution of pine–pine gall rust (Endocronartiumharknessii (J. P. Moore) Y. Hiratsuka) and pine–oak gall rust (Cronartiumquercuum (Berk) Miyabe ex Shirai f.sp. banksianae Burdsall and Snow) on jack pine (Pinusbanksiana Lamb.) throughout its range in Minnesota. Sporulating globose galls (960 galls from 257 stands) were collected in May and June and the pathogens were identified on the basis of aeciospore germ tube morphology. The relative usefulness of aeciospore germination characteristics that have been used to separate these rusts was examined. Endocronartiumharknessii predominated in the northeastern and Cronartiumquercuum in the southwestern portions of the range of jack pine. This information will be useful in selecting and growing rust-resistant trees and for monitoring changes in the distribution of these rusts in the future.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.